A journey into the wild of the cnidarian model system Aiptasia and its symbionts

C.R. Voolstra
Molecular Ecology, 22, pp. 4366-4368, (2013)

Keywords

Aiptasia, Cnidaria, Coral reefs, Symbiodinium, Symbiosis

Abstract

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​The existence of coral reef ecosystems relies critically on the
mutualistic relationship between calcifying cnidarians and
photosynthetic, dinoflagellate endosymbionts in the genus Symbiodinium.
Reef-corals have declined globally due to anthropogenic stressors, for
example, rising sea-surface temperatures and pollution that often
disrupt these symbiotic relationships (known as coral bleaching),
exacerbating mass mortality and the spread of disease. This threatens
one of the most biodiverse marine ecosystems providing habitats to
millions of species and supporting an estimated 500 million people
globally (Hoegh-Guldberg et al. 2007). Our understanding of
cnidarian–dinoflagellate symbioses has improved notably with the recent
application of genomic and transcriptomic tools (e.g. Voolstra et al.
2009; Bayer et al. 2012; Davy et al. 2012), but a model system that
allows for easy manipulation in a laboratory environment is needed to
decipher underlying cellular mechanisms important to the functioning of
these symbioses. To this end, the sea anemone Aiptasia, otherwise known
as a ‘pest’ to aquarium hobbyists, is emerging as such a model system
(Schoenberg & Trench 1980; Sunagawa et al. 2009; Lehnert et al.
2012). Aiptasia is easy to grow in culture and, in contrast to its stony
relatives, can be maintained aposymbiotically (i.e. dinoflagellate
free) with regular feeding. However, we lack basic information on the
natural distribution and genetic diversity of these anemones and their
endosymbiotic dinoflagellates. These data are essential for placing the
significance of this model system into an ecological context. In this
issue of Molecular Ecology, Thornhill et al. (2013) are the first to
present genetic evidence on the global distribution, diversity and
population structure of Aiptasia and its associated Symbiodinium spp. By
integrating analyses of the host and symbiont, this research concludes
that the current Aitpasia taxonomy probably needs revision and that two
distinct Aiptasia lineages are prevalent that have probably been spread
through human activity. One lineage engages in a specific symbiosis with
Symbiodinium minutum throughout the tropics, whereas a second, local
Aiptasia sp. population in Florida appears more flexible in partnering
with more than one symbiont. The existence of symbiont-specific and
symbiont-flexible Aiptasia lineages can greatly complement
laboratory-based experiments looking into mechanisms of symbiont
selectivity. In a broader context, the study by Thornhill et al. (2013)
should inspire more studies to target the natural environment of model
systems in a global context targeting all participating member species
when establishing ecological and genetic baselines.